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The 1991 season marked the introduction of the FIA’s new, and controversial, 3.5 Litre Formula which replaced the highly successful Group C category that had been used in the World Sportscar Championship since 1982. However, due to a small number of entries in the new 3.5 litre formula heavily penalised Group C cars were allowed participate in the newly created C2 category for the 1991 season but Jaguar participated in the new formula.

To comply with the new regulations Jaguar produced an all-new car, the XJR-14. It was designed by Ross Brawn and John Piper, and was built by Tom Walkinshaw Racing (TWR).[1] In the past, TWR's Jaguars had been designed under the direction of Tony Southgate, while Brawn worked with a large design staff (12 according to John Piper); a paradigm shift (albeit small) in its own right and reflective of Brawn's Formula One background.

The abandonment of the Group C fuel consumption regulations meant a change in aerodynamic design philosophy. Coupled that with vastly different packaging requirements for a small, light, normally aspirated engine meant that concerns over drag became a secondary requirement to downforce. The new design, lower kerb weight of 750 kg (1,653 lb) and higher downforce levels meant that the XJR-14 was a lot faster in corners compared to the previous Group C front runners.

The primary feature of the new regulations centred on 3.5 litre naturally aspirated engines. Although the XJR-14's predecessor, the XJR-11, used a twin turbo charged 3.5 litre engine derived from the Metro 6R4-derived JV6 engine, in order to comply with the new rules the two turbochargers would need to be removed. Naturally this wasn't a realistic option, nor was it ever considered, given the design compromises of not using a bespoke engine.

But given the Jaguar-Ford connection, it was a decided to utilise the 3.5 litre Ford HB V8 Formula One powerplant. Developed by Geoff Goddard and most notably used by the Benetton Formula One team, but now badged as a Jaguar, the Ford HB was detuned to about 11,500 rpm (compared to about 13,000 rpm) and aimed to produce slightly less power (about 650 bhp (485 kW) vs. around 700 bhp) with aims at enhanced reliability.

Three chassis were built and used for 1991: 591, 691, & 791. In the early part of the 1991 World Sportscar Championship season the XJR-14 was in a league of its own, totally outclassing its rivals and in particular the Peugeot 905 and Mercedes-Benz C291. Only the opening race went Peugeot's way, but that was seen more as a result of luck than the 905's competitiveness. The fact that Jaguar already had race proven engine certainly helped the team’s cause but the rest of the car was far superior to its rivals.

It wasn't until midway through the season that the Jaguar met its match through Peugeot's new 905B. This meant a hard fight with the new and quickly improving Peugeot squad for the rest of the season, but Jaguar was able to hold on and secure the manufacturers title with 3 victories.

At the 1991 24 Hours of Le Mans, Jaguar initially entered two XJR-14s but later decided that the XJR-14 would not be capable of finishing the distance due to unknowns in the development of the Cosworth HB to last 24 hours. Jaguar instead decided to enter three older XJR-12s which entered in the C2 class. Although the XJR-12s did not manage to win, Jaguar's decision not to run the untested XJR-14 was vindicated by the fact that Peugeot's 905 failed to finish the race. Mercedes also withdrew its C291 in favour of its older C11 models.

After 1991, Jaguar decided not to continue in Group C, believing that they had spent enough time in Group C and the instability of rules recently in the World Sportscar Championship. Jaguar decided to take the XJR-14 to the United States for the 1992 IMSA Camel GTP championship. However, without a major upgrade and with suspension that was not particularly well suited to the bumpier circuits in the championship, the XJR-14 was unable to beat the latest challengers from Toyota and Nissan, forced to finish third in the championship with only two victories. Jaguar continued to use the three updated 1991 chassis throughout the season.

Meanwhile, TWR had reached an agreement to supply more XJR-14 chassis to Mazda, minus the Cosworth V8s but installed with Mazda-badged Judd V10s for the World Sportscar Championship. Mazda would rebadge the XJR-14s as MXR-01s. The MXR-01 was essentially a productionised XJR-14 and as there had been no ongoing development they ended up not being particularly competitive, scoring no wins and finishing third in the championship.

Several years later, TWR would resurrect XJR-14 chassis #791, which had competed in IMSA Camel GTP, for the development of a new prototype for Porsche. They renamed the car the TWR-Porsche WSC-95. Its most significant feature was that it had the roof removed, turning it into an open cockpit prototype to run under the then-new LMP regulations. The WSC-95 would carry a Porsche 3.0L turbocharged Flat-6. After chassis #791 was modified, TWR built a second WSC-95 from scratch. In both the 1996 and 1997 24 Hours of Le Mans, the TWR-Porsches were able to take the overall win. See Chassis Log.